A pick-up truck has a cargo bed used to carry various cargos. Generally, the cargo bed is covered by a tonneau cover which is releasably clamped to and extended above the cargo bed, so as to protect the carried cargos from adverse weather and improve the aesthetic appearance of the pick-up truck. The tonneau covers can be classified into hard-top type and soft-top type, wherein the hard-top type tonneau cover has a hard top made of metal, fiberglass or the like, while the soft-top type tonneau cover has a soft top made of canvas, vinyl plastic or a weather-resistant fabric.
In general, although the hard-top tonneau cover provides greater security for cargo and can be more easily clamped on the cargo bed of the pick-up truck, it is heavier than the soft-top tonneau cover, and it needs more storage space for storing the hard-top tonneau cover after being removed from the pick-up truck. Furthermore, the soft-top tonneau cover is lighter in weight, and the volume thereof is more compact for storage. Meanwhile, both of the hard-top tonneau cover and the soft-top tonneau cover need to provide clamps for securely clamping the tonneau cover to the pick-up truck.
For example, referring now to FIG. 1, U.S. Patent Application Publication No. 2010-0270824 discloses a clamp structure for a tonneau cover 91, mounted to one of at least two frame sections 92 of the tonneau cover 91 for releasably securing the frame sections 92 on a side wall 93 of a cargo bed of a pick-up truck, the clamp comprises: a foundation rail 94 connected to one of the frame sections 92, and having two side grooves 941 formed on two side surfaces of the foundation rail 92, and a recess 942 formed between the two side grooves 941; a sliding block 95 having two side hangers 951 extended into the two side grooves 941 and slidably moving along the two side grooves 941, and a pivotal portion 952 received in the recess 942; a clamp bolt 96 having a first pivotal end 961 pivotally connected to the pivotal portion 952 of the sliding block 95, and a second pivotal section 962; a grip element 97 movably mounted on the clamp bolt 96 and having an engaging portion 971; and a handle 98 pivotally connected to the second pivotal section 962 of the clamp bolt 96 and having a cam surface 981 to abut against the grip element 97, so as to control the engaging portion 971 of the grip element 97 to engage with a surface of the side wall 93 of the pick-up truck.
In this traditional clamp structure, the grip element 97 is generally made of metal, engineering plastic or other equivalent rigid material. However, when the grip element 97 is only made of metal which is rigid without elastically deformable property, it is relatively difficult for the cam surface 981 of the handle 98 to smoothly abut against the grip element 97. Meanwhile, because the engaging portion 971 of the grip element 97 engages with the surface of the side wall 93 too tightly, there will be a risk of damaging the surface of the side wall 93. After long-term use, the cam surface 981, the grip element 97 and/or the surface of the side wall 93 may thus deform or be damaged, so as to increase the installation distance between the cam surface 981 and the grip element 97 or the engagement distance between the grip element 97 and the side wall 93, resulting in a loose or invalid clamping relationship thereof.
On the other hand, when the grip element 97 is only made of engineering plastic which has a certain elastically deformable property, the cam surface 981 of the handle 98 may abut against a pair of sliding grooves of the grip element 97 too tightly, so that the cam surface 981 of the handle 98 may accidentally depart from the sliding grooves (unlabeled) of the grip element 97. Meanwhile, because it has no sufficient structural strength for the engaging portion 971 of the grip element 97 to stably engage with the surface of the side wall 93, there will be a risk of damaging the engaging portion 971 of the grip element 97. After long-term use, the cam surface 981, the grip element 97 and/or the surface of the side wall 93 may thus deform or be damaged, so as to increase the installation/engagement distance and cause a loose or invalid clamping relationship.
As a result, it is important for related designers and manufacturers to think how to develop a clamp structure for a tonneau cover of a pick-up truck, in order to solve the problems existing in the conventional clamps, as described above.